Specialize IsMoveOnlyType<T> for vectors.

base/callback_internal.h

Index: base/callback_internal.h
diff --git a/base/callback_internal.h b/base/callback_internal.h
index e4e538ff15c2d0dfe239bc5d8b17fe411c59926e..643ea324404615f401ad47482d1422ea2f980178 100644
--- a/base/callback_internal.h
+++ b/base/callback_internal.h
@@ -11,6 +11,7 @@
 #include <stddef.h>
 #include <memory>
 #include <type_traits>
+#include <vector>

[dcheng, 2016/02/01 21:26:03]

Unfortunately, doing this means more opportunities for IWYU violations, since
callback.h is used pretty widely. But I don't think there's any way around this.

 
 #include "base/atomic_ref_count.h"
 #include "base/base_export.h"
@@ -118,6 +119,14 @@ template <typename T> struct IsMoveOnlyType {
 template <typename T, typename D>
 struct IsMoveOnlyType<std::unique_ptr<T, D>> : std::true_type {};
 
+// Specialization of std::vector, so that it's considered move-only if the
+// element type is move-only.
+template <typename T, typename Allocator>
+struct IsMoveOnlyType<std::vector<T, Allocator>> {
+  static const bool value =
+      IsMoveOnlyType<typename std::vector<T, Allocator>::value_type>::value;

[vmpstr, 2016/02/01 21:36:16]

FWIW, I think "typename std::vector<T, Allocator>::value_type" is an alias for
"T"

[dcheng, 2016/02/01 22:16:54]

The argument for using value_type is for consistency with associative containers
like map and unordered_map: we'd probably have another specialization for
std::pair, so we don't have to duplicate "if K or V is move-only, then entire
map is move only".

+};
+
 template <typename>
 struct CallbackParamTraitsForMoveOnlyType;